The present invention relates to a system for measuring the energy transfer between a heat exchanger and a fluid, such as air, moving through a conduit, such as a duct, in which the heat exchanger is located and, more particularly, to a system for ultrasonically sensing the temperature of the fluid on each side of the heat exchanger and for sensing the velocity of the fluid moving through the conduit so that the energy transfer across the heat exchanger can be determined.
The present cost of energy and the projection of energy costs into the future has increased the need for air conditioning systems which result in more savings in energy. Most present day air conditioning control systems, particularly automation systems, are equipped for energy management. Such energy management systems attempt to control conditions within the building at a level which is comfortable for the inhabitants of the building while at the same time minimizing the amount of energy necessary to maintain comfort within the building. Thus, such energy management systems must monitor the energy usage of the air conditioning system, conserve that energy, and, when desired by the user of the building, provide a report of the building's energy usage to the building user.
The measurement of energy usage in a building is the key for any successful energy management system. The process of heating and air conditioning in most building applications involves transfer of energy from air to water or from water to air. As an example, most large commercial buildings have a central chilling plant which chills water for distribution to rooms throughout the building. These rooms are supplied with air through ducts in which are located the fans to drive the air and the heat exchangers to either heat or cool the air. The water from the chiller then flows through the heat exchanger over which air is passed in order to cool the air for supply to the rooms. Similarly, in a heating application, the heating plant delivers hot water to the heat exchanger which then heats the air moving through the duct for supply to the rooms.
In order to accurately and adequately determine the energy which is being consumed in controlling the air at conditions which are comfortable for the occupants of the building, it is not only necessary to measure the amount of electricity and fuels for supplying the heating and chilling plants of the building, but it is also necessary to measure the heat transfer across the heat exchanger located within the ducts supplying treated air to the building. If this energy transfer is known, then it can be determined whether or not the water is cold enough or hot enough to satisfy the comfort level requirements of the building and whether or not the heating plant or the cooling plant is operating at an efficiency to minimize energy consumption and, therefore, energy cost. The present invention is directed to an arrangement for measuring the energy transfer across a heat exchanger located within an air conditioning duct in the building so that it can be determined how much energy is being transferred from the heat exchanger to the fluid or air moving through the duct.